Numerous data communication systems are available providing data message delivery. One such system having great popularity, the radio paging system, can deliver numeric and alphanumeric messages originated by a caller, using a telephone or an alphanumeric messaging terminal. The messages are then transmitted to a numeric or alphanumeric display pager. Radio paging systems deliver the messages using a variety of signaling formats, such as the Golay Sequential Code (GSC) and POCSAG signaling formats to small portable receivers referred to as pagers. The POCSAG signaling format is shown in FIG. IA. As shown, a synchronization code (SC) is first transmitted, which is used by all paging receivers, or pagers, within the system for maintaining synchronization with the transmitted information. The synchronization code (SC) is followed by eight frames, F1-F8. Each frame provides for the transmission of address blocks (A) and data blocks (M). Pagers are assigned to a specific one of the eight frames, providing the pager a battery saving function. The pagers are generally configured as tone-only pagers (T) responding only with an audible alert when paged, numeric pagers (N) responding with an audible alert and a displayed numeric message, such as a telephone number when pages, or alphanumeric pagers (Alpha) responding with an audible alert and a displayed alphanumeric message when paged. The paging system transmits only the address identifying the pager being paged for tone-only pagers, and an address identifying the pager to which a message is intended followed by the message for numeric and alphanumeric pagers. As shown in FIG. 1A, two tone-only address blocks can be transmitted in a single frame, while a simple seven digit phone number, which is encoded using a four bit binary data format, requires transmitting an address block followed by two data blocks, continuing part of the message into the next POCSAG frame. Alphanumeric messages, which are encoded using a seven bit BCH data format, can extend into many frames and required substantially more air time to transmit than either the tone-only or numeric pages. Consequently, the transmission of numeric and alphanumeric messages on a paging system reduced the number of pagers that can be loaded into the system, and this problem is compounded when long alphanumeric messages are transmitted. One solution which has been proposed for this problem is to increase the data transmission rate to 1200 bits per second from the current standard 512 bits per second. However, even this solution has proven inadequate for transmitting long data messages.
In order to obtain the message throughput required to handle long alphanumeric messages, substantially higher data rates, such as at 2400 or 4800 bits per second, or even higher are required. However, most paging systems in use today employ simulcast transmission of information to provide wide area coverage. Such paging systems employ a number of transmitters geographically separated, which are located in a cellular, or pseudo-cellular, fashion to provide the required coverage, and all transmitters transmit the same information simultaneously in all cells or zones. While conventional frequency modulated (FM) simulcast transmission systems can provide adequate message transmission at data rates below 2400 bits per second, they become difficult to set up and have not reliably been used to transmit messages at higher data rates. Problems, such as with providing proper phase equalization and synchronization of the transmission of the transmitters within the system become substantially more difficult at higher data rates.
Another problem that exists in the transmission of long messages, is insuring the message being transmitted, has been received by the pager for which it is intended, otherwise valuable air-time is wasted. Failure to receive the message can occur when the pager is out of range of the transmitters, has not been turned on by the user, has a dead battery, or has a battery that has died during the operating day. In providing a paging system capable of transmitting long messages, it is extremely important to know the messages being transmitted are likely to be received, otherwise valuable air-time is lost.